Planar waveguides are known that can combine discrete components on a single semiconductor substrate, such as a silicon wafer. The resulting devices can include many components on a single substrate for faster integration. Planar waveguides can be made by depositing a bottom cladding layer on a silicon substrate, depositing a core layer thereover, patterning the core layer and encapsulating the patterned core with a top cladding layer. The cladding and core layers are made of materials having different refractive indexes, such as differently doped silicon oxides for example. Light is confined in the patterned core.
FIG. 1 is directed to a conventional silicon waveguide. Referring to FIG. 1A, a silicon substrate 10 has a first or bottom cladding layer 12 thereon, having a refractive index. A core layer 14 having a different refractive index is deposited thereover, a mask layer 16 is deposited over the core layer 14 as shown in FIG. 1B. The core layer is then etched to the bottom of the cladding layer 12, which is then encapsulated with a second or top cladding layer 18, as shown in FIG. 1C. This layer can have the same or a different refractive index than the bottom cladding layer 12.
Thermo-optic switches, that can change the refractive index of the core and cladding layers by changing the temperature of the layers, are also known. These require some form of heating that can be connected to the waveguide, such as a power device or electrodes formed about an arm or layer of the device. A conventional thermo-optic attenuator is shown in FIG. 2. A light beam from an optical fiber 20 is connected to an optical waveguide 22 and divided into two light beams, A and B. One of the beams is heated by means of two electrodes 24 formed on the substrate 25, which creates a difference in the optical path length of the two beams A and B. The optical output power is based on the temperature difference between the two paths for beams A and B.
However, forming the electrodes adds several steps to the manufacture of the above device, and it would be desirable to form the heater in situ, without having to deposit and pattern the electrodes, and connect them to a source of power. The present methods can be used to make thermo-optical switches, attenuators and the like that are integrated with both passive and active devices on a single substrate.